The invention is directed to an electrostatic compressed air paint spray gun having a paint discharge nozzle connected to a paint delivery conduit and also having a compressed air discharge opening in the form of an apertured collar or annular gap concentrically surrounding the paint discharge nozzle. The compressed air discharge opening is connected to a compressed air delivery conduit and discharges adjacent to the paint discharge nozzle. The spray gun has an electrode arrangement connected to a high-voltage supply. Such electrostatic compressed air paint spray guns have been known for decades and are commercially available in a great variety of embodiments.
The structure of these electrostatic compressed air paint spray guns is comparatively simple. No rotatory drive and no rotating parts are required as compared to electrostatic rotation paint spray guns. The paint-carrying parts, valves and seals, are not subjected to any high pressure in contrast to airless high-pressure paint atomization because a paint pressure that guarantees a faultless conveying of the paint liquid up to the paint discharge nozzle is adequate; atomization and conveying of the paint ensue therefrom with the flowing compressed air. The compressed air is supplied by connection of the spray gun to a typical compressed air network; the pressure of approximately 6 through 8 bar usually present in these compressed air networks is fully adequate. The high-voltage for the electrodes is supplied either via a cable from a separate high-voltage generator or is generated with what is referred to as high-voltage cascades in the gun itself.
However, the excellent values for the precipitation efficiency and, in particular, for the paint compass obtained from electrostatic rotation paint spray guns generally cannot be achieved with the prior art electrostatic compressed air paint spray guns. It is recognized that one of the causes of this drawback is the higher kinetic energy of the atomized paint droplets in comparison to the rotation atomizer process of rotation paint spray guns. It has not been recognized that these disadvantages can be alleviated by controlling system parameters of compressed air atomization systems.